Given a string s made up of only lowercase letters, and a natural number k, remove any substring of length k from s so that the result is the lexicographically smallest possible word.
Input consists of several cases, each with s and k. Assume 1 ≤ k < | s | ≤ 104.
For every case, print the alphabetically smallest word that can be obtained after removing k consecutive letters from s.
abba 1 abba 2 abba 3 zxazyzy 3
aba aa a zxay